http://en.wikipedia.org/wiki/Last_Island,_Louisiana
LA is losing land at an extremely alarming rate and is definitely sinking. Anyone that doubts this has their head stuck in the mud. Read the above article. I now fish this spot that used to be called Last Island. It's a couple feet wide strip of grassy marshland.
Many of south LA's long time residents have seen for themselves how fast the land is disappearing. Almost everyone can tell you certain areas that are being swallowed by water.
Personally, I've seen the bayou in Dulac widen by about 6' in the last 20 years. The neighborhood that I grew up in Harvey, LA had homes beginning to sink due to the unstable ground, you could see it from the road. Anyone who doubts the truthfulness of the problems LA is facing needs to smacked!